Behavior of Ni atoms on the Cu(111) surface: A study by high-resolution electron-energy-loss spectroscopy

The temperature-dependent behavior of vapor-deposited Ni atoms on the Cu(111) surface has been studied by HREELS. Submonolayer coverage of Ni atoms are vapor-deposited on this surface in ultrahigh vacuum in the temperature range of 140--600 K. CO is used to monitor the structure of the Ni-covered Cu(111) surface at various Ni-deposition temperatures. For submonolayer Ni deposition at T=140 K, no significant diffusion of Ni atoms is observed. Above 150 K, Ni atoms begin to diffuse on the Cu(111) surface to form two-dimensional islands. At T>260 K, atomic exchange with the substrate atoms occurs and a mixed Ni-Cu monolayer is formed. Above 600 K, Cu atoms segregate to the surface and Ni atoms disappear completely from the top surface layer.